1. Field of the Invention
The present invention relates to a wavelength demultiplexer. More particularly, the present invention provides the wavelength demultiplexer with straight optical waveguide that minimizes the bending loss of optical waveguide caused in the wavelength demultiplexer.
2. Description of the Conventional Art
In order to meet series of consumers"" demand in information technology that increases day by day, high capacity and high-speed communication infrastructure are required. To fulfill such requirement, high-speed optical communications using optical fiber get popularized. However, in reality, switching systems of optical communication still depend on electronics components. To realize true high capacity and high-speed communication infrastructure, efficient optical switching systems need to be developed.
So far, light has been assumed to have one particular wavelength and many recent studies have been performed in the area of increasing the performance of the optical switching and routing device. Since wavelength division multiplexing technique was introduced, state of the art researches regarding optical communication has been concentrating on supplying multiplexed optical signals. Generally, materials used to implement wavelength demultiplexer are semiconductors, silica, and polymers. Among them, the widely used material to implement commercial wavelength demultiplexer is silica. Even though semiconductor has many advantages such that the demultiplexer implemented by semiconductor material may be integrated together with optical cross connector, multiplexer, and optical amplifier, it has a number of drawbacks like optical loss, and coupling loss. On the contrary, the silica demultiplexers have larger size than semiconductor demultiplexer does and monolithic integration with other devices is impossible. Nevertheless, the demultiplexer implemented by silica is widely used because internal loss and coupling loss of the waveguide is small.
If optical loss of the semiconductor demultiplexer can be reduced, semiconductor demultiplexer is to be used as a more efficient optical device.
The important points in the process of demultiplexing are low cross talk and efficient elimination of optical attenuation. The major problem of the conventional demultiplexers in wavelength division multiplexing implementation is optical loss at the output.
In large, there are three losses in loss category of the wavelength demultiplexer. They are material loss, structural loss, and insertion loss. Under the structural loss, there are waveguide propagation loss and loss from optical power splitter. The lengths of optical waveguides of the conventional wavelength demultiplexers differ with respect to different channels in order to reduce such losses. As a result, optical path length difference occurs and thereby each channel is to have waveguide bending structure of different bending radius of curvature from other channels. In other words, it is inevitable for the conventional wavelength demultiplexers to have optical waveguide bending structure.
Due to these bending losses, cross talk gets worse and thereby the implementation of semiconductor demultiplexer suffers. Moreover, due to the optical waveguide bending structure, overall size of the wavelength demultiplexer is big.
1. U.S. Patent Documents
U.S. Pat. No. 5,751,872, May 12, 1998, Wavelength demultiplexer
U.S. Pat. No. 5,243,672, Sep. 07, 1993, Planar waveguide having optimized bend
U.S. Pat. No. 5,675,675, Oct. 07, 1997, Bandwidth-adjusted wavelength demultiplexer
2. Other Publications
IEEE Photonics Technology Letters, Vol. 10, No. 3, March 1998, pp. 379xcx9c381, J. C. Chen et al., xe2x80x9cA Proposed Design for Ultra low Loss Waveguide Grating Routersxe2x80x9d.
IEEE Photonics Technology Letters, Vol. 10, No. 3, March 1998, pp. 382xcx9c384, C. G. M. Vreeberg et al., xe2x80x9cA Low-loss 16 Channel Polarization dispersion-compensated PHASAR Demultiplexerxe2x80x9d.
IEE Electronics Letters, Vol. 30, No. 4, February 1994, pp. 300xcx9c302, M. R. Amersfoort et al., xe2x80x9cPhased-array Wavelength Demultiplexer with flattened wavelength Responsexe2x80x9d.
IEEE Conference Proceedings of 11th LEOS Annual Meeting, Orlando, Fla., 1998, pp317-pp318, K-S, Hyun, B.-S, Yoo, and M.-H, Cho, xe2x80x9c8 Channel Dispersion-controlled Phased Array Demultiplexer in InP/InGaAsPxe2x80x9d.
A wavelength demultiplexer with straight optical waveguide comprises an optical power distributor, a plurality of optical waveguides, and an optical power combiner. The optical power distributor evenly divides multiplexed input light by intensity. The number of optical waveguide transmits the divided multiplexed light and causes constant optical path length differences among adjacent waveguides. The optical waveguide is straight optical waveguide and includes two parts of different effective refractive indices. The optical power combiner receives output signals of the plurality of optical waveguides and separates the output signals by phase.
Desirably, two parts of different effective refractive indices in straight optical waveguide comprise two materials of different refractive indices.
Desirably, the two materials of different refractive indices are InGaAsP and InAlAsP.
Desirably, the straight optical waveguide comprises two parts of different waveguide widths.
Desirably, the two parts further comprises transition region of adiabatic transition to suppress reflection and mode change caused by refractive index difference at the edge of said two parts.
Desirably, the straight optical waveguides have unique difference in length of the two parts, the difference in length of the two parts in a straight optical waveguide being determined by following equation
xcex94Lk=n1l1k,k+1+n2l2k,k+1
where xcex94Lk is the optical path length difference of optical waveguides, n1 is the effective refractive index of material 1, n2 is the effective refractive index of material 2, l1k,k+1 is the difference in length of adjacent optical waveguides of material 1, and l2k,k+1 is the difference in length of adjacent optical waveguides of material 2.